The present invention relates to a storage system used for a computer system, and more particularly the present invention relates to a method of expanding a volume capacity at the time of writing into a storage system from a computer system.
Generally, a computer system is comprised of a computer that performs each individual job and a storage device that reads and writes data in accordance with a command of the computer. The storage device has a plurality of physical disks to store and read out data, and manages the physical disks by dividing into a plurality of storage areas.
Accordingly, the storage device can provide the storage area to the computer in a form of a logical volume. This logical volume is comprised of a plurality of segments and is a unit of a logical storage capacity that makes it possible to read and write data in accordance with the command of the computer by allocating the storage area on the physical disk to each segment. The capacity of this logical volume can be expanded at any time according to a necessity.
For example, when the computer uses up the logical volume provided by the storage device, the computer can expand the logical volume capacity by creating a logical volume from an unused storage area of a physical disk in the storage device and by combining this logical volume with the logical volume in use. Such a method is called on-line volume expansion.
However, in this on-line volume expansion, an administrator of the storage device needs to perform a series of operations until the volume expansion is completed. Therefore, when a sudden increase of the capacity occurs in computer systems of a plurality of enterprises in such a large scale data center that the plurality of enterprises use simultaneously, there occurs a possibility that requests for on-line volume expansion are generated simultaneously such that the administrator of the storage device is not able to cope with. In the worst case, there has been such a problem that it was not possible to perform the on-line volume expansion and processing of the computer stopped.
Then, in order to solve a request of a user and administrator of a storage system, the patent reference 1, for example, discloses such a method that a storage device creates a storage area from an unused area in a physical disk while a computer is on-line and adds dynamically to a segment of a logical volume during on-line access when a capacity of the logical volume in the storage device becomes insufficient due to writing from the computer. Such method is called a volume capacity automatic expansion.
This volume capacity automatic expansion is to make an allocation of an unallocated area of a physical disk to a logical volume when there is a request for writing from a computer. The on-line volume expansion can be automatically performed without an intervention of an administrator of a storage device by this volume capacity automatic expansion.
[Patent Reference 1] Japanese Patent Application Publication No. 2003-15915